Danielle Raats

Intravital Microscopy Through an Abdominal Imaging Window Reveals a Pre-Micrometastasis Stage During Liver Metastasis

An abdominal imaging window allows in vivo visualization of dynamic cellular processes, including liver metastasis and islet cell transplantation. Peering Into Cancer Understanding what goes on inside the body, as it is happening, is an ongoing challenge in medical imaging. Conventional imaging methods are only “snapshots,” unable to truly capture biology in action or the progression of disease. In this study by Ritsma and colleagues, an abdominal imaging window (AIW) proves to be the answer, allowing the authors to visualize and quantify metastatic processes in real time, in vivo in mice. The AIW consisted of a titanium ring with a glass coverslip, which could be tightly secured to the abdominal wall of a mouse. This window stayed in place for an average of 5 weeks, which is long enough to visualize many biological phenomena, including single-cell activity in the small intestine, spleen, pancreas, and kidney, as demonstrated by Ritsma et al. Although able to image many organs and cells, the authors chose to focus on tumor cell metastasis—specifically, the metastasis of mouse colorectal cancer C26 cells to the liver. By tracking fluorescently labeled C26 cells over the course of 2 weeks, the authors were able to confirm that the majority of metastatic growth was clonal (that is, from a single founder cell) rather than synergistic. The authors also noticed that the cancer cells had different phenotypic properties at different time points: At day 3, the cells were motile and diffuse in the liver tissue, whereas, at day 5, the cells stopped moving and were densely packed. The authors called this phenotypic shift a “pre-micrometastatic” state, followed by the “micrometastatic state.” Blocking cell migration in the pre-micrometastatic stage with a small-molecule inhibitor reduced cell growth and formation of subsequent micrometastases. Ristma and coauthors have developed a powerful in vivo imaging tool to track biological events in real time. This will hopefully lend insight into many diseases that affect abdominal organs. Although their preliminary findings suggest a new target for pharmacological inhibition of cancer growth and migration, additional preclinical and clinical studies will be needed to follow up this pre-micrometastatic hypothesis and to further confirm its presence in humans. Cell dynamics in subcutaneous and breast tumors can be studied through conventional imaging windows with intravital microscopy. By contrast, visualization of the formation of metastasis has been hampered by the lack of long-term imaging windows for metastasis-prone organs, such as the liver. We developed an abdominal imaging window (AIW) to visualize distinct biological processes in the spleen, kidney, small intestine, pancreas, and liver. The AIW can be used to visualize processes for up to 1 month, as we demonstrate with islet cell transplantation. Furthermore, we have used the AIW to image the single steps of metastasis formation in the liver over the course of 14 days. We observed that single extravasated tumor cells proliferated to form “pre-micrometastases,” in which cells lacked contact with neighboring tumor cells and were active and motile within the confined region of the growing clone. The clones then condensed into micrometastases where cell migration was strongly diminished but proliferation continued. Moreover, the metastatic load was reduced by suppressing tumor cell migration in the pre-micrometastases. We suggest that tumor cell migration within pre-micrometastases is a contributing step that can be targeted therapeutically during liver metastasis formation.

Oncogenic K-Ras Turns Death Receptors Into Metastasis-Promoting Receptors in Human and Mouse Colorectal Cancer Cells

BACKGROUND & AIMS Death receptors expressed on tumor cells can prevent metastasis formation by inducing apoptosis, but they also can promote migration and invasion. The determinants of death receptor signaling output are poorly defined. Here we investigated the role of oncogenic K-Ras in determining death receptor function and metastatic potential. METHODS Isogenic human and mouse colorectal cancer cell lines differing only in the presence or absence of the K-Ras oncogene were tested in apoptosis and invasion assays using CD95 ligand and tumor necrois factor-related apoptosis-inducing ligand (TRAIL) as stimuli. Metastatic potential was assessed by intrasplenic injections of green fluorescent protein- or luciferase-expressing tumor cells, followed by intravital fluorescence microscopy or bioluminescence imaging, and confocal microscopy and immunohistochemistry. Ras-effector pathway control of CD95 output was assessed by an RNA-interference and inhibitor-based approach. RESULTS CD95 ligand and TRAIL stimulated invasion of colorectal tumor cells and liver metastases in a K-Ras-dependent fashion. Loss of mutant K-Ras switched CD95 and TRAIL receptors back into apoptosis mode and abrogated metastatic potential. Raf1 was essential for the switch in CD95 function, for tumor cell survival in the liver, and for K-Ras-driven formation of liver metastases. K-Ras and Raf1 suppressed Rho kinase (ROCK)/LIM kinase-mediated phosphorylation of the actin-severing protein cofilin. Overexpression of ROCK or LIM kinase allowed CD95L to induce apoptosis in K-Ras-proficient cells and prevented metastasis formation, whereas their suppression protected K-Ras-deficient cells against apoptosis. CONCLUSIONS Oncogenic K-Ras and its effector Raf1 convert death receptors into invasion-inducing receptors by suppressing the ROCK/LIM kinase pathway, and this is essential for K-Ras/Raf1-driven metastasis formation.

Salmeterol with fluticasone enhances the suppression of IL-8 release and increases the translocation of glucocorticoid receptor by human neutrophils stimulated with cigarette smoke

The combination of inhaled corticosteroids and long-acting β2-adrenoceptor agonists is increasingly used in chronic obstructive pulmonary disease (COPD). Recently, we have demonstrated that combination of salmeterol and fluticasone propionate (FP) additionally suppress the production of IL-8 by human monocyte. In this study, the molecular mechanism behind the effectiveness of this combination therapy is investigated in human neutrophils. Human neutrophils were preincubated with salmeterol or FP or the combination. The amount of interleukin-8 (IL-8), elastase and matrix metalloproteinases (MMP)-2 and -9 releases, and reactive oxygen species (ROS) generation and expression of MAP kinase phosphatase (MKP-1) and glucocorticoid receptor (GR) were determined. Cigarette smoke medium (CSM) induces an increased expression of CXC receptors and the production of ROS that may explain the strong production of IL-8 by neutrophils. The expression of CXC receptors, the production of ROS, and the release of elastase and MMP-2 and -9 were not influenced by salmeterol, FP, or the combination. Interestingly, the combination therapy had an additive suppressive effect on the CSM-induced production of IL-8. The latter could be explained by an increased mRNA expression of MKP-1, the GR and an increased translocation of the GR to the nucleus. This leads eventually to suppression of both the NF-κB and MAPK pathways and, hence, to less IL-8 production by the neutrophil. These data are in support for the use of a combination therapy in COPD patients.

The death receptor CD95 activates the cofilin pathway to stimulate tumour cell invasion

The death receptor CD95 promotes apoptosis through well‐defined signalling pathways. In colorectal cancer cells, CD95 primarily stimulates migration and invasion through pathways that are incompletely understood. Here, we identify a new CD95‐activated tyrosine kinase pathway that is essential for CD95‐stimulated tumour cell invasion. We show that CD95 promotes Tyr 783 phosphorylation of phospholipase C‐γ1 through the platelet‐derived growth factor receptor‐β, resulting in ligand‐stimulated phosphatidylinositol (4,5)‐bisphosphate (PIP2) hydrolysis. PIP2 hydrolysis liberates the actin‐severing protein cofilin from the plasma membrane to initiate cortical actin remodelling. Cofilin activation is required for CD95‐stimulated formation of membrane protrusions and increased tumour cell invasion.

Cigarette smoke stimulates the production of chemokines in mast cells.

Chronic obstructive pulmonary disease is a major health problem and will become the third largest cause of death in the world by 2020. It is currently believed that an exaggerated inflammatory response to inhaled irritants, in particular, cigarette smoke (CS), causes the progressive airflow limitation, in which macrophages and neutrophils are attracted by chemokines, leading to oxidative stress, emphysema, small airways fibrosis, and mucus hypersecretion. Smoking is also associated with an increase in mast cell numbers in bronchial mucosa. This study was conducted to determine the direct effects of CS on mast cell function, using murine bone marrow‐derived mast cells (BMMC) as an in vitro model. BMMC were cultured from BALB/cBy mice for 3 weeks. Cells were treated with CS medium (CSM) for 30 min or 16 h. The effects of CSM on mast cell degranulation and chemokine production were measured. Moreover, we investigated the effect of CSM on IκB‐α degradation and p38, Erk1/2, p65, and CREB expression by Western blotting. We found that CSM stimulated the release of chemokines in a noncytotoxic manner but did not induce mast cell degranulation. CSM induced phosphorylation of Erk1/2, p38, and CREB and increased translocation of p65 without degradation of IκB‐α NF‐κB in mast cells. The induction of chemokine production by CSM in mast cells could promote and prolong the inflammatory process. Our observations suggest that mast cells may contribute to the pathogenesis of emphysema through a direct effect of CS on the production of proinflammatory chemokines.

Oncogenic KRAS sensitises colorectal tumour cells to chemotherapy by p53-dependent induction of Noxa

Background:Oxaliplatin and 5-fluorouracil (5-FU) currently form the backbone of conservative treatment in patients with metastatic colorectal cancer. Tumour responses to these agents are highly variable, but the underlying mechanisms are poorly understood. Our previous results have indicated that oncogenic KRAS in colorectal tumour cells sensitises these cells to chemotherapy.Methods:FACS analysis was used to determine cell-cycle distribution and the percentage of apoptotic and mitotic cells. A multiplexed RT–PCR assay was used to identify KRAS-controlled apoptosis regulators after exposure to 5-FU or oxaliplatin. Lentiviral expression of short-hairpin RNAs was used to suppress p53 or Noxa.Results:Oncogenic KRAS sensitised colorectal tumour cells to oxaliplatin and 5-FU in a p53-dependent manner and promoted p53 phosphorylation at Ser37 and Ser392, without affecting p53 stabilisation, p21 induction, or cell-cycle arrest. Chemotherapy-induced expression of the p53 target gene Noxa was selectively enhanced by oncogenic KRAS. Suppression of Noxa did not affect p21 induction or cell-cycle arrest, but reduced KRAS/p53-dependent apoptosis after exposure to chemotherapy in vitro and in tumour xenografts. Noxa suppression did not affect tumour growth per se, but strongly reduced the response of these tumours to chemotherapy.Conclusion:Oncogenic KRAS determines the cellular response to p53 activation by oxaliplatin or 5-FU, by facilitating apoptosis induction through Noxa.

Synergistic killing of colorectal cancer cells by oxaliplatin and ABT-737

BackgroundOxaliplatin is frequently used in the treatment of metastatic colorectal cancer (CRC). Our previous work shows that oxaliplatin induces the pro-apoptotic protein Noxa in CRC cells. The Bcl2-inhibitor ABT-737 is particularly effective in cells with high Noxa levels. Therefore, we tested whether oxaliplatin and ABT-737 display synergy in killing CRC cells.MethodsA panel of CRC cell lines was treated with oxaliplatin and ABT-737, either alone or in combination. Apoptosis was measured by FACS analysis of sub-G1 DNA content and by Western blot analysis of caspase-3 processing. Noxa expression was suppressed by lentiviral RNA interference.ResultsOxaliplatin and ABT-737 displayed a strong synergistic apoptotic response, which was dependent on wildtype TP53 and oncogenic KRAS. TP53 and KRAS were required for drug-induced Noxa expression and this was essential for tumor cell apoptosis. Oxaliplatin, but not ABT-737, induced p53 accumulation, but both drugs stimulated Noxa expression. Combination treatment of mice with subcutaneous tumor xenografts drastically reduced tumor volume, while single drug treatment had no effect.ConclusionABT-737 synergizes with oxaliplatin to kill colorectal cancer cells. This requires induction of Noxa by wildtype TP53 and oncogenic KRAS. Future studies should explore the anti-tumor efficacy of this drug combination in mouse models for spontaneous CRC development and in patient-derived tumor cell cultures and xenografts.

Maintenance of Clonogenic KIT+ Human Colon Tumor Cells Requires Secretion of Stem Cell Factor by Differentiated Tumor Cells

BACKGROUND & AIMS Colon tumors contain a fraction of undifferentiated stem cell-like cancer cells with high tumorigenic potential. Little is known about the signals that maintain these stem-like cells. We investigated whether differentiated tumor cells provide support. METHODS We established undifferentiated colonosphere cultures from human colon tumors and used them to generate stably differentiated cell lines. Antibody arrays were used to identify secreted factors. Expression of genes involved in stemness, differentiation, and the epithelial to mesenchymal transition was measured using reverse transcription quantitative polymerase chain reaction. Expression of KIT in human tumors was analyzed with gene expression arrays and by immunohistochemistry. Colonospheres were injected into the livers of CBy.Cg-Foxn1nu/J mice. After liver tumors had formed, hypoxia was induced by vascular clamping. RESULTS Differentiated cells from various tumors, or medium conditioned by them, increased the clonogenic capacity of colonospheres. Stem cell factor (SCF) was secreted by differentiated tumor cells and supported the clonogenic capacity of KIT(+) colonosphere cells. Differentiated tumor cells induced the epithelial to mesenchymal transition in colonosperes; this was prevented by inhibition of KIT or SCF. SCF prevented loss of clonogenic potential under differentiation-inducing conditions. Suppression of SCF or KIT signaling greatly reduced the expression of genes that regulate stemness and the epithelial to mesenchymal transition and inhibited clonogenicity and tumor initiation. Bioinformatic and immunohistochemical analyses revealed a correlation between expression of KIT- and hypoxia-related genes in colon tumors, which was highest in relapse-prone mesenchymal-type tumors. Hypoxia induced expression of KIT in cultured cells and in human colon tumor xenografts and this contributed to the clonogenic capacity of the tumor cells. CONCLUSIONS Paracrine signaling from SCF to KIT, between differentiated tumor cells and undifferentiated stem-like tumor cells, helps maintain the stem-like features of tumor cells, predominantly under conditions of hypoxia.

Oncogenic K-Ras Activates p38 to Maintain Colorectal Cancer Cell Proliferation during MEK Inhibition

Background: Colon carcinomas frequently contain activating mutations in the K-ras proto-oncogene. K-ras itself is a poor drug target and drug development efforts have mostly focused on components of the classical Ras-activated MEK/ERK pathway. Here we have studied whether endogenous oncogenic K-ras affects the dependency of colorectal tumor cells on MEK/ERK signaling. Methods: K-ras mutant colorectal tumor cell lines C26, HCT116 and L169 were used. K-ras or components of the MEK/ERK and p38 pathway were suppressed by RNA interference (RNAi). MEK was inhibited by U0126. p38 was inhibited by SB203850. Results: MEK inhibition, or suppression of MEK1/2 or ERK1/2 by RNA interference, reduced the proliferation rate of all colorectal cancer cell lines. However, cell proliferation returned to normal after two weeks of chronic inhibition, despite the continued suppression of MEK or ERK. In contrast, K-ras-suppressed tumor cells entered an irreversible senescent-like state following ERK pathway inhibition. MEK inhibition or ERK1/2 suppression caused activation of p38α in a K-ras-dependent manner. Inhibition or suppression of p38α prevented the recovery of K-ras mutant tumor cells during prolonged MEK inhibition. Conclusions: Oncogenic K-ras activates p38α to maintain cell proliferation during MEK inhibition. MEK-targeting therapeutics can create an acquired tumor cell dependency on p38α.

Macrophages induce “budding” in aggressive human colon cancer subtypes by protease-mediated disruption of tight junctions

Primary human colorectal tumors with a high stromal content have an increased capacity to metastasize. Cancer-associated fibroblasts (CAFs) promote metastasis, but the contribution of other stromal cell types is unclear. Here we searched for additional stromal cell types that contribute to aggressive tumor cell behavior. By making use of the ‘immunome compendium’—a collection of gene signatures reflecting the presence of specific immune cell-types—we show that macrophage signatures are most strongly associated with a high CAF content and with poor prognosis in multiple large cohorts of primary tumors and liver metastases. Co-culturing macrophages with patient-derived colonospheres promoted ‘budding’ of small clusters of tumor cells from the bulk. Immunohistochemistry showed that budding tumor clusters in stroma-rich areas of T1 colorectal carcinomas were surrounded by macrophages. In vitro budding was accompanied by reduced levels of the tight junction protein occludin, but OCLN mRNA levels did not change, nor did markers of epithelial mesenchymal transition. Budding was accompanied by nuclear accumulation of β-catenin, which was also observed in budding tumor cell clusters in situ. The NFκB inhibitor Sanguinarine resulted in a decrease in MMP7 protein expression and both NFκB inhibitor Sanguinarine and MMP inhibitor Batimastat prevented occludin degradation and budding. We conclude that macrophages contribute to the aggressive nature of stroma-rich colon tumors by promoting an MMP-dependent pathway that operates in parallel to classical EMT and leads to tight junction disruption.